Concrete is made using a cementitious binder, aggregates (e.g., sand and coarse stone), water, and optionally one or more chemical admixtures for modifying slump (a rheological property), strength, and/or other properties. The slump of the concrete can be increased by adding water. However, too much water can lead to decreased compressive strength in the resultant concrete when hardened.
It is known that the “slump” of concrete in ready-mix delivery trucks can be controlled by using sensors to monitor the energy required for rotating the mixing drum, such as by monitoring the torque applied to the drum by measuring hydraulic pressure and adjusting fluidity by adding fluid into the mixing drum. Examples of fluid dispensing systems are disclosed in U.S. Pat. Nos. 4,008,093 and 5,713,663.
Various automated slump monitoring systems having fluid dispensing capability are described for background purposes as follows. The term “automated slump monitoring” will be used herein to include systems that measure the concrete on a continuous basis and modify the slump of the concrete through dispensing of water, chemical admixture, or both.
In U.S. Pat. No. 4,356,723 (1982), Fay taught that the hydraulic pressure required for rotating the mix drum, when measured at constant rotation speed, provided an indication of slump state, and taught that this could be measured at the building site when the concrete was to be discharged. The operator could add water from a tank on the truck during loading, transit, or delivery using a valve, and the slump could be adjusted at delivery. See e.g., U.S. '723 at column 4, lines 3 et seq.
In U.S. Pat. No. 4,318,177, Rapp et al. disclosed that water addition to concrete can be controlled through empirical testing of consistency by initially feeding a quantity of water to the batch reduced by an amount equivalent to the moisture content of the aggregates of the batch at maximum intrinsic moisture content, and thereafter incrementally adding measured amounts of water while measuring consistency after each water addition, and storing these values for the respective recipe and batch size.
In U.S. Pat. No. 4,544,275, Hudelmaier taught a system for automatically closing the water supply valve on the mixing truck when the drive torque applied to the mixing drum exceeded an adjustable limit. For special conditions, such as a change in climate, the system could also provide for opening of a water supply valve for admitting a limited, preselected amount of water. See e.g., Abstract of '275 patent.
In U.S. Pat. No. 5,713,663, Zandberg et al. disclosed a mixing truck wherein the hydraulic drive for rotating the mixing drum was monitored and liquid component was added into the concrete to approach a predetermined minimum torque loading on the hydraulic drive. A water volume sensor was provided to measure the amount of water added to the concrete. The prevention of excess liquid additions could also be controlled using this apparatus.
In U.S. Pat. No. 5,752,768, Assh disclosed a system for calculating slump of concrete in a mixer and for calculating the amount of water required to change from the current slump to a target slump for the purpose of deciding how much water to add into the concrete to increase the slump.
In U.S. Pat. No. 6,484,079), Buckelew emphasized the need for automated monitoring and reporting of the slump of the concrete to a remote location, such as the dispatch center, due to driver mistakes or other occasions in which water was intentionally added to the concrete and not reported. For example, Buckelew noted that sometimes the foreman at the delivery site would often request that water be incorporated into the concrete to ease installation; drivers could be persuaded to add water before pouring and to avoid reporting the water addition (See column 2, lines 11-24). Buckelew attempted to resolve this problem by providing a status sensor and measuring the current slump and comparing this to a delivery slump, as well as a water counter for determining the amount of water added to the concrete. Data regarding this delivery status could be transmitted to the dispatch center. Buckelew did not provide a means for determining whether the slump information indicated a change in fluid content or other variations in the concrete.
In U.S. Pat. No. 8,082,431 (which is owned by the common assignee hereof), Cooley et al. disclosed a delivery vehicle system having a hydraulic sensor coupled to the hydraulic drive and configured to sense hydraulic pressure required to turn the mixing drum and a rotational sensor configured to sense the rotational speed of the mixing drum. The system contained flow valves and flow meters for measuring and controlling water or chemical admixture addition into the concrete.
In U.S. Pat. No. 8,118,473 (which is owned by the common assignee hereof), Compton et al. disclosed a delivery vehicle system wherein a sensing of the rotational speed of the concrete mixing drum is used to qualify a calculation of current slump based on the hydraulic pressure required to turn the mixing drum. This system also contained flow valves and meters which could be controlled by computer to measure and control the amount of water added to the mixing drum to reach a desired slump, and may also obtain data on water manually added to the mixing drum by a hose connected to the truck water supply via a separate flow sensor or from a status system (See column 5, lines 9-22).
In Ser. No. 12/993,844, Berman disclosed a concrete mixing control apparatus with a sensor mounted on the interior surface of a concrete mixer drum and configured to monitor stress or pressure, which could be related to concrete slump. The system further comprised a liquid flow meter. Berman further disclosed a method of determining the amount of water needed to adjust the current slump to the target slump and then adding this amount of water.
In U.S. Ser. No. 13/500,643, Beaupre et al. disclosed a rheological probe for mounting inside a rotating mixing drum and configured to sense drum speed and force, and using collected data from the probe to determine slump and other rheological properties of the concrete.